Sintered polycrystalline gallium nitride and its production

Abstract

Polycrystalline gallium nitride (GaN) characterized by having the atomic fraction of gallium ranging from between about 49% to 55%, an apparent density of between about 5.5 and 6.1 g/cm 3 , and a Vickers hardness of above about 1 GPa. Polycrystalline GaN can be made by hot isostatic pressing (HIPing) at a temperature ranging from about 1150° C. to 1300° C. and a pressure ranging from between about 1 and 10 Kbar. Alternatively, polycrystalline GaN can be made by high pressure/high temperature (HP/HT) sintering at a temperature ranging from about 1200° to 1800° C. and a pressure ranging from about 5 to 80 Kbar.

1. Polycrystalline gallium nitride (CaN), having an apparent density of between about 5.5 and 6.1 g/cm 3 , a Vickers hardness of above about 1 GPa, eguiaxed grains with an average size of between about 0.01 and 50 μm, and wherein the atomic fraction of gallium ranges from between about 49% to 55%. 
     
     
       2. The GaN of  claim 1 , which has a thickness or minimum dimension of between about 0.2 mm and 1 m. 
     
     
       3. The GaN of  claim 1 , which has a diameter or maximum dimension of between about 1 mm and 1 m. 
     
     
       4. The CaN of  claim 1 , having surfaces that are substantially smooth, with a root-mean-square roughness below about 100 μm. 
     
     
       5. The GaN of  claim 4 , having surfaces that are substantially smooth, with a root-mean-square roughness below about 20 μm. 
     
     
       6. A method for making sintered polycrystalline gallium nitride (GaN), which comprises the steps of:
 (a) enclosing and sealing GaN as one or more of powder or a cold-pressed pill, in a non-metallic container;  
 (b) subjecting said container to hot isostatic pressing (HIPing) at a temperature ranging from about 1150° C. to 1300° C. and a pressure ranging from between about 1 and 10 Kbar; and  
 (c) recovering polycrystalline GaN from said container.  
 
     
     
       7. The method of  claim 6 , wherein said non-metallic container is evacuated of air prior to sealing. 
     
     
       8. The method of  claim 6 , wherein said HIPing is conducted for a time ranging from about 2 minutes to about 24 hours. 
     
     
       9. The method of  claim 6 , wherein said recovering step includes grinding off the container from said sintered polycrystalline GaN. 
     
     
       10. The method of  claim 6 , wherein said sintered polycrystalline GaN has a thickness or minimum dimension of between about 0.2 mm and 1 m. 
     
     
       11. The method of  claim 6 , wherein said sintered polycrystalline GaN has a diameter or maximum dimension of between about 1 mm and 1 m. 
     
     
       12. The method of  claim 6 , wherein said sintered polycrystalline GaN has equiaxed grains with an average size of between about 0.01 and 50 μm. 
     
     
       13. The method of  claim 6 , wherein said sintered polycrystalline GaN has surfaces, which are substantially smooth, with a root-mean-square roughness below about 100 μm. 
     
     
       14. The method of  claim 13 , wherein said sintered polycrystalline GaN has surfaces, which are substantially smooth, with a root-mean-square roughness below about 20 μm. 
     
     
       15. The method of  claim 6 , wherein said GaN enclosed in said container is a powder. 
     
     
       16. The method of  claim 6 , wherein said GaN enclosed in said container is a cold-pressed pill. 
     
     
       17. A method for making sintered polycrystalline gallium nitride (GaN), which comprises the steps of:
 (a) placing GaN as one or more of powder or a cold-pressed pill in a high pressure/high temperature (HP/HT) reaction cell;  
 (b) placing said reaction cell in a HP/HT apparatus;  
 (c) subjecting said container to a temperature ranging from about 1200° to 1800° C. and a pressure ranging from about 5 to 80 Kbar; and  
 (d) recovering polycrystalline GaN from said reaction cell.  
 
     
     
       18. The method of  claim 17 , wherein step (c) is conducted for a time ranging from about 2 minutes to about 24 hours. 
     
     
       19. The method of  claim 17 , wherein said recovering step includes grinding. 
     
     
       20. The method of  claim 17 , wherein said sintered polycrystalline GaN has a thickness or minimum dimension of between about 0.2 mm and 1 m. 
     
     
       21. The method of  claim 17 , wherein said sintered polycrystalline GaN has a diameter or maximum dimension of between about 1 mm and 1 m. 
     
     
       22. The method of  claim 17 , wherein said sintered polycrystalline GaN has equiaxed grains with an average size of between about 0.01 and 50 μm. 
     
     
       23. The method of  claim 17 , wherein said sintered polycrystalline GaN has surfaces, which are substantially smooth, with a root-mean-square roughness below about 100 μm. 
     
     
       24. The method of  claim 23 , wherein said sintered polycrystalline GaN has surfaces that are substantially smooth, with a root-mean-square roughness below about 20 μm. 
     
     
       25. The method of  claim 17 , wherein said GaN enclosed in said container is a powder. 
     
     
       26. The method of  claim 17 , wherein said GaN enclosed in said container is a cold-pressed pill.